lockfile: move REPORT_ON_ERROR bit elsewhere

There was LOCK_NO_DEREF defined as 2 = 1<<1 with the same value,
which was missed due to a huge comment block.  Deconflict by moving
the new one to 4 = 1<<2 for now.

Signed-off-by: Junio C Hamano <gitster@pobox.com>

lockfile.h

@@ -137,7 +137,7 @@ struct lock_file {
  * ... this flag can be passed instead to return -1 and give the usual
  * error message upon an error.
  */
-#define LOCK_REPORT_ON_ERROR 2
+#define LOCK_REPORT_ON_ERROR 4
 
 /*
  * Usually symbolic links in the destination path are resolved. This